Watson may be able to recommend you get surgery, but he won't be able to perform the surgery himself. He's only moving in on one aspect of medicine. Matching symptoms to diagnoses is the thing that machines are most clearly suited for in the entire medical profession, because of the vast volume of possible measurements and diagnoses, and because humans' various cognitive biases don't work well with the probabilistic nature of the work. That's still a rather narrow range of work. Humans will remain superior at performing medical work for quite a while. And until true Strong AI, humans will also remain superior for quite a large amount of gathering information that Watson requires, especially psychological measurements, and for making decisions that involve quality-of-life and other ethical considerations beyond just probability of success.

tl;dr Watson can, and will, exceed doctor's capability for a certain, somewhat narrow, range of their function. Doctors will still be necessary for the other things that they do.